Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Thermochemical structures beneath Africa and the Pacific Ocean

Abstract

Large low-velocity seismic anomalies have been detected in the Earth's lower mantle beneath Africa and the Pacific Ocean that are not easily explained by temperature variations alone1,2,3,4,5,6,7,8,9,10,11. The African anomaly has been interpreted to be a northwest–southeast-trending structure3,4,5,7 with a sharp-edged linear, ridge-like morphology9,10. The Pacific anomaly, on the other hand, appears to be more rounded in shape1,2,3,4,6,7,11. Mantle models with heterogeneous composition have related these structures to dense thermochemical piles or superplumes12,13,14,15,16,17,18,19. It has not been shown, however, that such models can lead to thermochemical structures that satisfy the geometrical constraints, as inferred from seismological observations. Here we present numerical models of thermochemical convection in a three-dimensional spherical geometry using plate velocities inferred for the past 119 million years20. We show that Earth's subduction history can lead to thermochemical structures similar in shape to the observed large, lower-mantle velocity anomalies. We find that subduction history tends to focus dense material into a ridge-like pile beneath Africa and a relatively more-rounded pile under the Pacific Ocean, consistent with seismic observations.

Your institute does not have access to this article

Relevant articles

Open Access articles citing this article.

Access options

Buy article

Get time limited or full article access on ReadCube.

$32.00

All prices are NET prices.

Figure 1: Perspective views of two tomography models 4,7 and geodynamic compositional fields at the end of the calculations, corresponding to the present day.
Figure 2: Temperature and tomography maps.
Figure 3: Effect of initial condition.

References

  1. Su, W. & Dziewonski, A. M. Simultaneous inversion for 3-D variations in shear and bulk velocity in the mantle. Phys. Earth Planet. Inter. 100, 135–156 (1997)

    ADS  Article  Google Scholar 

  2. Breger, L. & Romanowicz, B. Three-dimensional structure at the base of the mantle beneath the central Pacific. Science 282, 718–720 (1998)

    ADS  CAS  Article  Google Scholar 

  3. Ritsema, J., van Heijst, H. J. & Woodhouse, J. H. Complex shear wave velocity structure imaged beneath Africa and Iceland. Science 286, 1925–1928 (1999)

    CAS  Article  Google Scholar 

  4. Ritsema, J., van Heijst, H. J. & Woodhouse, J. H. Global transition zone tomography. J. Geophys. Res. 109, doi:10.1029/2003JB002610 (2004)

  5. Kuo, B. Y., Garnero, E. J. & Lay, T. Tomographic inversion of S-SKS times for shear velocity heterogeneity in D″: degree 12 and hybrid models. J. Geophys. Res. 105, 28139–28157 (2000)

    ADS  Article  Google Scholar 

  6. Masters, G., Laske, G., Bolton, H. & Dziewonski, A. in Earth's Deep Interior: Mineral Physics and Tomography from the Atomic to the Global Scale (eds Karato, S. et al.) 63–87 (Geophys. Monogr. Ser., Vol. 117, AGU, Washington DC, 2000)

    Book  Google Scholar 

  7. Grand, S. P. Mantle shear-wave tomography and the fate of subducted slabs. Phil. Trans. R. Soc. Lond. A 360, 2475–2491 (2002)

    ADS  Article  Google Scholar 

  8. Wen, L., Silver, P., James, D. & Kuehnel, R. Seismic evidence for a thermo-chemical boundary at the base of the Earth's mantle. Earth Planet. Sci. Lett. 189, 141–153 (2001)

    ADS  CAS  Article  Google Scholar 

  9. Ni, S., Tan, E., Gurnis, M. & Helmberger, D. Sharp sides to the African superplume. Science 296, 1850–1852 (2002)

    ADS  CAS  Article  Google Scholar 

  10. Ni, S. & Helmberger, D. V. Seismological constraints on the South African superplume: Could be the oldest distinct structure on Earth. Earth Planet. Sci. Lett. 206, 119–131 (2003)

    ADS  CAS  Article  Google Scholar 

  11. Ishii, M. & Tromp, J. Constraining large-scale mantle heterogeneity using mantle and inner-core sensitive normal modes. Phys. Earth Planet. Inter. 146, 113–124 (2004)

    ADS  Article  Google Scholar 

  12. Tackley, P. J. in The Core-Mantle Boundary Region (eds Gurnis, M., Wysession, M. E., Knittle, E. & Buffett, B. A.) 231–253 (Geodyn. Ser. Vol. 28, AGU, Washington DC, 1998)

    Book  Google Scholar 

  13. Davaille, A. Simultaneous generation of hotspots and superswells by convection in a heterogeneous planetary mantle. Nature 402, 756–760 (1999)

    ADS  CAS  Article  Google Scholar 

  14. Kellogg, L. H., Hager, B. H. & van der Hilst, R. D. Compositional stratification in the deep mantle. Science 283, 1881–1884 (1999)

    ADS  CAS  Article  Google Scholar 

  15. Tackley, P. J. Mantle convection and plate tectonics: toward an integrated physical and chemical theory. Science 288, 2002–2007 (2000)

    ADS  CAS  Article  Google Scholar 

  16. Davaille, A., Girard, F. & Le Bars, M. How to anchor hotspots in a convecting mantle? Earth Planet. Sci. Lett. 203, 621–634 (2002)

    ADS  CAS  Article  Google Scholar 

  17. Jellinek, A. M. & Manga, M. The influence of a chemical boundary layer on the fixity, spacing, and lifetime of mantle plumes. Nature 418, 760–763 (2002)

    ADS  CAS  Article  Google Scholar 

  18. Jellinek, A. M. & Manga, M. Links between long-lived hot spots, mantle plumes, D″, and plate tectonics. Rev. Geophys. 42, doi:10.1029/2003RG000144 (2004)

  19. Tackley, P. J. Strong heterogeneity caused by deep mantle layering. Geochem. Geophys. Geosyst. 3, 1024, doi:10.1029/2001GC000167 (2002)

    ADS  Article  Google Scholar 

  20. Lithgow-Bertelloni, C. & Richards, M. A. The dynamics of Cenozoic and Mesozoic plate motions. Rev. Geophys. 36, 27–78 (1998)

    ADS  Article  Google Scholar 

  21. McNamara, A. K. & Zhong, S. Thermochemical structures within a spherical mantle: Superplumes or piles? J. Geophys. Res. 109, B07402, doi:10.1029/2003JB002847 (2004)

    ADS  Article  Google Scholar 

  22. Bunge, H. P. et al. Timescales and heterogeneous structure in geodynamic Earth models. Science 280, 91–95 (1998)

    ADS  CAS  Article  Google Scholar 

  23. Bunge, H. P., Richards, M. A. & Baumgardner, J. R. Mantle-circulation models with sequential data assimilation: inferring present-day mantle structure from plate-motion histories. Phil. Trans. R. Soc. Lond. A 360, 2545–2567 (2002)

    ADS  Article  Google Scholar 

  24. Zhong, S., Zuber, M. T., Moresi, L. & Gurnis, M. Role of temperature-dependent viscosity and surface plates in spherical shell models of mantle convection. J. Geophys. Res. 105, 11063–11082 (2000)

    ADS  Article  Google Scholar 

  25. Mitrovica, J. X. & Forte, A. M. A new inference of mantle viscosity based upon joint inversion of convection and glacial isostatic adjustment data. Earth Planet. Sci. Lett. 225, 177–189 (2004)

    ADS  CAS  Article  Google Scholar 

Download references

Acknowledgements

We thank C. Lithgow-Bertelloni and T. Becker for furnishing us with the plate velocity data used in these calculations. We also thank J. Ritsema and E. Garnero for discussions and for help in generating figures for this manuscript. This work was supported by the David and Lucile Packard Foundation and the National Science Foundation.

Author information

Authors and Affiliations

Authors

Corresponding author

Correspondence to Allen K. McNamara.

Ethics declarations

Competing interests

Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

McNamara, A., Zhong, S. Thermochemical structures beneath Africa and the Pacific Ocean. Nature 437, 1136–1139 (2005). https://doi.org/10.1038/nature04066

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nature04066

Further reading

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing